1. Field of the Invention
The present invention relates to a tracking gain control method, and more particularly a tracking gain control method for an optical pickup for reading the signals on optical discs from a plurality of standards with each having a different reflectivity.
2. Description of the Related Art
In an optical disc apparatus for recording information onto and reading information from optical discs, the optical pickup scans the track on an optical disc with laser light. A tracking servo control is performed at the optical pickup so that the laser light follows the track on the optical disc rotating at high speed. The tracking servo control is performed on the basis of a tracking error signal that indicates the amount of deviation of the laser light from the track. The tracking error signal is output by an optical sensor for detecting the reflected light from the optical disc.
Generally, the servo loop gain of the tracking servo control performs control operations to track the amplification gain of a voltage control amplifier (VCA) that is provided with an automatic gain control circuit (AGC) for maintaining a constant intensity of the light intensity signal (RF signal). Therefore, when the light intensity signal is small, the tracking gain is raised, and when the light intensity signal is large, the tracking gain is lowered.
For example, for optical discs having a diameter of 130 mm (5.25 inches) and a common track pitch (recording track spacing) and minimum pit length (minimum length of a recording pit), various standards are available besides CD, such as CD-R, CR-RW, and so forth. Since these optical discs use different materials for their reflecting film, in comparison to the 70% or higher reflectivity of the laser light for the CD standard, it is 65% or higher for CD-R media and approximately 20% for CD-RW media.
If a single optical pickup is used to read signals from optical discs having different standards, the tracking gain increases since the light intensity signal decreases for optical discs having a lower reflectivity than that of CD media, such as CD-R, CD-RW, and so forth. When the tracking gain increases excessively, one problem is that the tracking servo loop circuit may become unstable during a track jump operation thereby impairing playability.